Carcass characteristics, meat quality, and nutritional profiles of Mithun (Bos frontalis) meat reared under a semi-intensive system

2.1 Experimental animals and feeding

The study was conducted at the Mithun breeding farm, ICAR-National Research Centre on Mithun, Medziphema, Nagaland, India (25°54′30″ north latitude and 93°44′15″ east longitude, altitude 300 m from mean sea level). Experimental Mithuns (n = 16) consisting of males and females (body condition score 5–6 out of 10; classified as “good”) were selected and divided into four groups, MM-4 (n = 4, male, <4 years of age, body weight 361 ± 23 kg [mean ± SEM]), MM-47 (n = 4, male, 4–7 years of age, body weight 472.75 ± 30 kg), MF-4 (n = 4, female, <4 years of age, body weight 276.25 ± 18 kg), and MF-47 (n = 4, female, 4–7 years of age, body weight 348.50 ± 12 kg).

The Mithuns were maintained under semi-intensive and isomanagerial conditions and fed according to the ICAR (2013) feeding standards with a dry matter intake of 2.5% of body weight. Animals were fed in the morning with two kilograms of concentrate mixture (87%–88% dry matter [DM], 16%–18% crude protein, 55%–60% total digestible nutrients and 11. 65 MJ/kg DM metabolizable energy) fortified with mineral mixture and salt. Thereafter, animals were let loose (09:00–15:00 h) with free access to the forest foliage. Once animals returned from grazing, they were provided ad libitum mixed fodder (paddy straw [50%] + Napier and Congo signal grass [50%]) and drinking water.

2.2 Slaughter and carcass characteristics

Mithuns were transported to the modern abattoir of the Municipal Council of Dimapur, Nagaland, India, for the slaughter in the late evening, rested for 12 h with ad libitum water, and were slaughtered the next day morning. Uniformly dressed carcasses were evaluated for carcass traits individually within an hour after slaughter (Figure S1), namely, carcass length (measured in centimeters on the ventral surface from the pubic bone to the anterior rim of the first rib), and right half of the carcass was divided into standard primal cuts and left half deboned for determining the meat yield (%), fat (%), bone (%), and meat-to-bone ratio. After the separation, cuts were weighed, and percentages of different cut yields were calculated for bone, muscle, and fat. Carcass parameters—namely, live weight (fasted live weight in kg), the weight of carcass (kg), carcass length in centimeters (anterior rim of the first rib to the pubic bone) (Figure S2), dressing percentage, head with horn (%), hide (%), hoof and feet (%), meat (%) (deboned), fat (%), bone (%), meat-to-bone ratio, and wholesale cuts—were recorded according to Meat and Livestock Commission standards (Boniface, 1991).

The percentage of forequarter (chuck, rib, foreshank, brisket and short plate) and hindquarter (round, short loin, sirloin, flank, yield of offal, lungs and trachea, heart, liver, kidney, and spleen) were calculated. For the rib eye area/loin eye area, the impressions were taken on trace paper by exposing the 12th rib, and the impression area was measured using a graph paper (cm²). Visible marbling (degree of marbling or intramuscular fat) was measured (rib eye area) at the 12th rib cross-section and compared with a standard photograph of marbling scoring guide by visual appraisal (National Nutrient Database for Standard Reference Release, USDA, 2016) (Figure S3). Marbling was assigned to one of the categories (moderately abundant, slightly abundant, moderate, modest, small, and slight) (Figure S4).

2.3 Meat quality evaluation

Muscle (longissimus thoracis: triplicate samples) was collected from each Mithun carcass and stored at refrigeration temperature (4 ± 1°C) for 24 h packed in the 200-G low-density polyethylene (LDPE) bags for the completion of rigor mortis. Later, separable fat and connective tissue were removed, portioned, packed in 200-G LDPE bags, and frozen (−20 ± 1°C) until further processing. The meat sample was thawed at 4 ± 1°C for 12 h before analysis, ground in a mincer (Santos, France), packed in polyethylene terephthalate (PET) jars, and stored under refrigeration (4 ± 1°C) until the required parameters were evaluated.

2.4 Sensory characteristics

A six-membered panel comprising staff of ICAR-NRC on Mithun, Medziphema Nagaland, India, was trained according to the standard guidelines and briefed about different sensory attributes and the nature of the experiment without disclosing the identity of samples. Sensory evaluation was based on an 8-point hedonic scale (Keeton, 1983) with modifications (Figure S5), where an 8 score was excellent and 1 score was extremely poor. Meat chunks (cube of 3 cm) from four different Mithun groups were mixed with 1.5% salt and water (50% of meat) in a glass beaker (250 ml) and covered with aluminum foil. The water in a pressure cooker was up to one fourth of the height of the beaker. The glass beakers containing meat samples were then placed in the pressure cooker. Cooking was done under the high flame until the first whistle and then turned to cook under simmering for 30 min. The cooked samples were separated from the meat extract, cooled to room temperature, and then subjected to sensory evaluation. Panelists evaluated the samples for appearance, flavor, juiciness, tenderness, connective tissue residue, and overall acceptability using the standard score sheet. Filtered water was provided to the panelists for rinsing their mouths in between the evaluations of different samples. Mean scores for different groups were recorded and statistically analyzed.

2.5 Statistical analysis

The experiments were undertaken in triplicates (n = 4 × 3 observations in each group except for carcass characteristics) and data generated for different quality characteristics were compiled and analyzed using SPSS (version 20.0 for Windows; SPSS, Chicago, IL, USA). The individual animal data of each group were pooled and tested for normality before analysis using Shapiro–Wilk statistics, and the outliers were removed. The data of different parameters (between the groups) were analyzed by one-way analysis of variance (ANOVA) and Tukey's test as a post hoc test. The percent data were transformed into radians before analysis by one-way ANOVA. The results are presented as mean values ± SEM and considered statistically significant only when P < 0.05.

3.1 Carcass characteristics

The carcass characteristics of male and female Mithuns slaughtered at different age groups are presented in Table 1. Significantly higher (P < 0.05) live weights were noted in males (MM-4 and MM-47) compared to females, attributed to the higher growth rates in male Mithuns than in females. Previous reports indicated that male Mithun calves exhibit greater growth rates and nutrient intakes than their female counterparts (Pal et al., 2004). Males exhibited significantly higher (P < 0.05) carcass weights compared to females (MM-47, followed by MM-4, MF-47, and MF-4). Higher carcass weights are indicative of increased muscling and fat depositions (Sañudo et al., 1997). A similar study on buffaloes found that males slaughtered at 2.5 years of age had higher carcass weights than females (Ekiz et al., 2018). Carcass length in males exceeded that in females, although the recorded lengths were slightly lower compared to previous studies (Mondal et al., 2001). Dressing percentages remained consistent across different age and sex groups, but an increase was noted with age in males from 49.67% in MM-4 to 52% in MM-47. Earlier research (Das et al., 2012; Mondal et al., 2001) reported higher dressing percentages (58%–62%) in both male and female Mithuns. Another study indicated a dressing percentage of 54%, inclusive of offals (Bhattacharyya et al., 2007). In contrast, Mondal et al. (2014) reported dressing percentages ranging from 48% to 54% in Mithuns slaughtered at various age groups. Dressing percentage, meat percentage, and carcass meat yield are vital metrics for assessing slaughter performance, with variations potentially attributed to factors such as season, breed, fat score, and muscle score (Coyne et al., 2019).

In this study, male Mithuns exhibited a greater percentage of head with horns compared to females, aligning with findings from Mukherjee et al. (2014). These values slightly surpass those reported in crossbred bovines (Pasha & Malik, 1990). Marginal distinctions were noted in hide percentage, hoof and feet percentage, and percentages of deboned meat and bone across the groups. Females (MF-4 and MF-47) exhibited a significantly higher (P < 0.05) fat percentage compared to males (MM-4 and MM-47). Typically, females tend to accumulate more fat than males, as observed in sheep (Díaz et al., 2003) and cattle (Fiems et al., 2003). The greater fat deposition with advancing age may be attributed to nutrient availability and the growth of skeletal muscles, leading to a substantial increase in body fat (Cockrill, 1985). Males (MM-4 and MM-47) displayed a significantly higher (P < 0.05) meat-to-bone ratio than females (MF-4 and MF-47). The increase in meat yield with age is a recognized pattern in bovines (Li et al., 2018).

The results of standard cuts are presented in Table 1 and Figure S6. The proportion of wholesale cuts, encompassing forequarter and hindquarter, exhibited no variations among the groups. These proportions aligned with those observed in buffalo (Lambertz et al., 2014) and cattle (Lapitan et al., 2007). Offal yields displayed no differences among the groups, consistent with results obtained in cattle and buffalo (Lapitan et al., 2007). Rib eye area did not differ among the groups, except for the higher values in males compared to females. This observation corresponds with Kondaiah et al. (1983), who noted a larger eye muscle area (17.40 cm²) in male buffaloes than in females (15.62 cm²). The intramuscular fat content and marbling score in all groups ranged from “slight” to “small” (Table S1; Figures S7 and S8). Reduced intramuscular fat content is indicative of limited marbling, which is a characteristic feature in Mithun carcasses. In this study, older animals with heavier carcasses displayed small marbling, whereas younger animals with lower carcass weights exhibited slight marbling. The tendency for marbling to increase with age aligns with findings in male buffaloes, where it demonstrates a strong correlation with the animals' live weights (Li et al., 2018).

3.2 Meat quality characteristics

The physicochemical properties of Mithun meat from different groups are presented in Table 2. The meat pH exhibited higher values in younger animals, a trend similarly noted by Kiran et al. (2016), who observed significantly elevated pH (6.22) in young buffaloes. Variation in the pH might be due to the variation in muscle glycogen reserves and differences in the postmortem aerobic and anaerobic metabolism or even response to transport stress in younger and older Mithuns. The WHC was slightly higher in younger Mithuns compared to older ones and slightly higher in males than in females. This pattern is consistent with findings in young buffaloes compared to their older counterparts (Kandeepan et al., 2009). Enhanced WHC in young Mithuns is associated with improved juiciness, as WHC is closely linked to tenderness and juiciness. Moreover, the role of muscle pH in meat WHC is noteworthy, with higher pH levels indicating greater WHC (Purchas, 1990).

In this study, the myoglobin content in adult Mithuns was significantly higher (P < 0.05) than in younger Mithuns. Meat becomes darker and reddish with increasing age due to the increase in concentrations of the myoglobin pigment. In Mithun, the meat pigments in younger individuals were significantly lower (P < 0.05) than in older counterparts. This shift toward darker meat color with age is a common phenomenon in bovines, attributed to the increased concentration of meat pigment, specifically myoglobin (Kandeepan et al., 2009). SSP content was greater in males and older animals, and the percentage of SSP was higher in Mithuns compared to buffaloes (Kandeepan et al., 2009). Conversely, water-soluble proteins exhibited no significant differences (P > 0.05) among the groups, although values were slightly elevated in adult Mithuns. Older animals typically display higher water-soluble protein levels compared to younger ones, as reported in buffaloes (Kiran et al., 2016). The MF-47 exhibited significantly higher cooking loss (P < 0.05), and the lower cooking loss percentage in younger Mithuns may be attributed to their higher meat pH. The correlation between cooking losses and pH is negative, as indicated by previous studies (Purchas, 1990). The overall cooking loss increased with the age of the animal, indicating increased protein denaturation or increased collagen cross-linking. This leads to reduced WHC and increased moisture loss during cooking (Schönfeldt & Strydom, 2011).

The MFI was significantly higher (P < 0.05) in the meat of young Mithuns compared to that of older counterparts. A lower MFI in older Mithun meat suggests increased toughness, possibly due to reduced myofibrillar protein fragmentation capability (Morgan et al., 1993). The age of the animal exhibited a significant effect on muscle fiber diameter, with lower values (P < 0.05) observed in young Mithuns. Muscle fiber diameter tends to increase with age; in buffaloes, age influences muscle fiber diameters rather than the sex of the animal (Nuraini et al., 2013). Muscle fiber diameter is positively correlated with shear force values but negatively related to muscle tenderness (Biswas et al., 1989). The WBSF indicated significantly higher (P < 0.05) shear force values in the meat of older Mithuns compared to younger ones. The increased muscle fiber diameter, smaller sarcomere length, and relatively lower MFI in older bovines are associated with elevated WBSF values, indicating greater toughness (Kandeepan et al., 2009).

3.3 Nutritional profiling of Mithun meat

The proximate composition of Mithun meat obtained in different groups is presented in Table 3. Meat from young male Mithuns exhibited significantly higher (P < 0.05) moisture content compared to other groups. The decline in moisture content with age is likely associated with an increase in fat content. Protein content in the meat from different groups did not show significant differences and fell within the range of 22.55%–23.84%, indicating that Mithun meat is a substantial source of animal protein. A prior study reported a protein content of 19.58% in Mithun meat (Mondal et al., 2001). In this study, the protein content of Mithun meat increased with age, consistent with findings in other bovine species (Li et al., 2018). Additionally, meat from females (MF-4 and MF-47) demonstrated significantly higher (P < 0.05) fat content compared to males (MM-4 and MM-47), a trend also observed by Sami et al. (2004) where meat from older female buffaloes showed higher (P < 0.01) fat content. The current results indicate that Mithun meat is leaner than meats from other animal species, with relatively low fat content, potentially attributed to poor marbling.

The ash content of Mithun meat fell within the range of 1.02%–1.15%, and crude ash did not exhibit age-related changes (Li et al., 2018). Table 4 summarizes the fatty acid profile of Mithun meat, with no significant (P > 0.05) differences observed in the fatty acid content. Mithun meat is notably rich in polyunsaturated fatty acids (PUFA); a study on buffalo indicated PUFA levels in the range of 1.75%–3.15% (Luz et al., 2017). Typically, monounsaturated fatty acids and PUFA make up approximately 40%–50% and 10%–20%, respectively, of the total fatty acids in fresh meat products (Schönfeldt & Strydom, 2011). The values observed in Mithun meat align closely with this established range. Meat from free-range animals tends to have higher PUFA levels; for example, free-range bison demonstrated higher PUFA content compared to feedlot bison (Rule et al., 2002). In the current study, Mithuns were allowed to graze for a brief period, contributing to the observed higher PUFA content.

The essential and nonessential amino acid profiles of Mithun meat in different groups are presented in Table 5 with no significant differences in values between groups. Mithun meat is a good source of essential abundant (lysine and leucine) and nonessential (glutamic, aspartic acid, arginine and alanine) amino acids. Concentrations of amino acids were higher in the Mithun meat compared to other bovine species (Samicho et al., 2013).

The cholesterol content in Mithun meat ranged from 32.53 to 44.27 mg/100 g (Table 6), with significantly higher (P < 0.05) levels in female Mithuns, and this could be attributed to their higher fat contents that increased with the advancement of slaughter age. The cholesterol content (mg/100 g) in the present study was found lower than values reported for bison (43.8) (Rule et al., 2002), buffalo (43.71–57.42) (Luz et al., 2017), and cattle (Giuffrida-Mendoza et al., 2015). Further, the energy value in male Mithun meat was significantly lower (P < 0.05) for MM-4 than for MF-4 and MF-47 (Table 6). Higher calorie value in female meat could be attributed to higher fat content. Earlier studies indicated that meat from females with higher total calorie content than castrates and intact males (Johnson et al., 1995). The calorie values in this study ranged from 101 to 112 kcal/100 g, comparable to or slightly lower than reported values for buffalo meat, cattle beef, and mutton (Aziz et al., 2014; Pereira & Vicente, 2013; Williams, 2007).

The vitamin content of Mithun meat is presented in Table 6, and no significant (P > 0.05) differences were observed in the water-soluble vitamin content between the groups. The thiamine (vitamin B1) content ranged from 0.46 to 0.75 mg/100 g, surpassing levels found in beef, veal, and chevon (Williams, 2007). For riboflavin (vitamin B2), Mithun meat exhibited a range of 1.17–1.88 mg/100 g, exceeding values in beef and chevon (Williams, 2007). Niacin (vitamin B3) content in Mithun meat varied from 3.44 to 4.11 mg/100 g, consistent with earlier reports in Mithun and comparable to beef (Longvah et al., 2017; Williams, 2007). Older Mithuns showed higher vitamin concentrations, aligning with findings that older animals tend to have elevated vitamin levels (Purchas et al., 2007).

Mineral profiles of Mithun meat are presented in Table 6, and no significant differences (P > 0.05) were observed between the groups. The copper content ranged from 0.20 to 0.31 mg/kg, which was lower than levels found in beef, veal, lamb, and mutton (Chan et al., 1995). Zinc content in Mithun meat (2.72–3.00 mg/100 g) was comparable to values reported for beef and Polish red beef (Domaradzki et al., 2016; USDA, 2016). The iron content ranged from 1.73 to 2.14 mg/100 g, aligning with earlier reports in Mithun and similar to buffalo meat, beef, pork, and Polish red beef (Domaradzki et al., 2016; Longvah et al., 2017; USDA, 2016). Sodium content (24.51–34.03 mg/100 g) was lower than previous reports on Mithun meat chops and also lower compared to beef, pork, and Polish red beef (Domaradzki et al., 2016; Longvah et al., 2017; USDA, 2016). Calcium content ranged from 4.08 to 6.64 mg/100 g, similar to earlier reports on Mithun meat chops and comparable to lean beef and Polish red beef (Domaradzki et al., 2016; Longvah et al., 2017; Williams, 2007). The magnesium content varied between 12.80 to 14.75 mg/100 g, lower than previous reports on Mithun chops, beef, Polish red beef, and pork (Domaradzki et al., 2016; Longvah et al., 2017; Williams, 2007). Variations in mineral compositions were attributed to factors such as species, breed, feeding regimen, season, and meat cut (Williams, 2007).

3.4 Sensory characteristics

Table 7 presents the sensory characteristics of Mithun meat, with no significant differences (P > 0.05) in appearance, flavor, and overall acceptability scores among different groups. However, a significant (P < 0.05) difference was observed for juiciness, tenderness, and connective tissue residue for age groups only. Appearance and flavor scores fell within the “good” to “very good” range and were consistent across all groups. Overall acceptability scores, also in the “good” to “very good” range, indicated favorable organoleptic attributes. Juiciness, tenderness, and connective tissue residue scores were significantly higher (P < 0.05) in older animals compared to younger ones, attributed to increased fiber diameter, connective tissue, and cross-linkages between polypeptide chains with age. Huff and Parrish (1993) also reported that carcasses of older animals were juicier (P < 0.05) than carcasses of young bulls and steers. Tenderness scores were significantly (P < 0.05) higher in younger animals, attributed to decreased activation of μ-calpain in older animals (Morgan et al., 1993). Tenderness plays a crucial role in consumer satisfaction, with studies on beef also noting mature animals to be less tender than their younger counterparts (Smith et al., 1982). Connective residue scores, indicating the amount of insoluble connective tissue post-chewing, significantly (P < 0.05) increased with the age of Mithun meat.

In conclusion, the present study is the first-ever attempt to study the carcass characteristics, meat quality, physicochemical properties, nutritional composition, and sensory characteristics of Mithun at different ages and between sexes. Fat (%) was higher, and deboned meat (%) was lower in MF-4 and MF-47, while marginal differences were observed in bone (%), dressing percentage, and offal yield between the groups. Younger Mithuns had higher pH and water holding capacity, affecting cooking yield. Older Mithuns exhibited darker meat due to elevated myoglobin and total pigment content, though appearance scores were unaffected. Older Mithuns had lower tenderness scores attributed to a lower myofibrillar index, increased muscle fiber diameter, and higher shear force. Fat percentage and cholesterol content were significantly higher in female Mithuns. Protein content was consistent across groups, with no significant differences in nutritional profiles. The effect of age was found to impact juiciness, tenderness, and connective tissue residue scores. Sensory evaluation indicated the “very good” organoleptic acceptability of the cooked Mithun meat. This study indicated that Mithun meat is a rich source of protein, amino acids, PUFA, water-soluble vitamins, and minerals with low-fat content regardless of age and sex.